Need Help determining a relay

Hey, I currently have a circuit that has two separate loops that need to be shut off when a temp switch loop is broken. I don’t have electrical experience, so I was wondering if anyone knew what type of relay I would need. Is there a DPDT relay that can open two circuits when its signal is broken? Or would this be better to do with two separate relays with the same signal?


Akb515, welcome to the Digikey TechForum.

I have narrowed a list of search results to show you what products are available with the requirements you have let me know about so far.

Click here to see them

Can I ask you what voltage and current your load is expected to be and how would you like this to mount?

Voltage will be 12V, not completely sure about the current, but I’m expecting < 3 or 4A.

Can I wire those relays as shown in my diagram?

I have narrowed the list a little bit further.
Click here to see them

I would like to explain one thing here. You technically would only need to have a DPST relay. That would mean that you would have two switches being switched with signal. Each of those switches would have only one contact to switch to.

You would also have to choose if you want those internal switches to be normally on or normally closed. This is the state it is in when there is not any signal present. Your request implies that you would want it to be normally closed. This way when your temp sensor goes down, so does your load.

with that being said, a DPDT type of relay allows you to choose as each switch as terminals for the activated state as well as the deactivated state. These are the options in the link above.

Gotcha! Thank you! So just to confirm, I’d need a single DPST relay? Yeah, the temp sensor loop will normally be closed, and when the range is too high or too low, it will open the loop.

You are correct. You just need to make sure that you have a Normally Closed contact (NC) version or it will work the opposite way.

I see there is not much for options for DPST-NC
click for options

In comparison to the DPDT options
click for options

I hope this helps!

Perfect, thanks!

You will need a DPST-NO relay. That will shut off the 2 loops when the temp loop is broken.
A DPST-NC will close (activate) the 2 loops when the temp loop is broken. You can use a DPDT relay, and you will have both the Normally Open and Normally Closed contacts.

David is correct on this one. I am sorry I got that switched around in my mind.

When the temp sensor has a closed circuit, it will in turn activate the coil on the relay which closes the circuits on both switches. In order for that to be activated and closed, it would first have to be in a deactivated state or “open”. Thank you David for correcting me.

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Thanks for the catch! Will do!